Lymphocytes form six HTLV-I/II seropositive donors were co-cultured with PHA stimulated lymphocytes and grown in medium containing 10% interleukin-2. Cultures from three donors were maintained for 3 weeks and the cells were harvested and DNA extracted for PCR analysis. Co-cultures from the other three donors were maintained for up to four months. Cells were harvested at 3, 4, 12, 14 and 16 weeks and DNA extracted for PCR analysis. DNA was amplified with HTLV-I GAG primer pairs, GP1/Gp2, HTLV-II POL primer pairs, SK58/SK59 and SK110/SK111, HTVL-II ENV primer pairs, SG638/SGS39 and HTLV-II LTR primer pairs, LT1/LT2. The amplified DNA was hybridized with oligoprobes GP3 (HTIV-I GAG); SK60, SK188 (HTLV-II POL), SG640 (HTLV-II ENV) and LT3 (HTLV-II, LTR). Results of PCR analysis showed that all cultures contained HTLV-II viral genome. PCR analysis of RNA from two cultures showed positive amplification with HTLV-II primer pairs suggesting for the expression of viral genes in these cultures. Co-culture of lymphocytes enhanced the detection of viral gene sequences.